The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Primary cementing in a cased oil, gas, or water well is the process of placing cement in the annulus between the casing and the formations through which the wellbore passes. The major objective is to provide zonal isolation, which is the prevention of fluid flow between different formation layers. Various materials may be added to the cement to enhance the performance and/or to improve the economics. Recent development of heavy oil reserves using heat (for example using steam) have placed additional stresses on the cement sheath, which may compromise the zonal isolation achieved with existing cement slurries.
Steam injection methods have been implemented to maximize recovery of heavy oil deposits in many fields worldwide. Several approaches have been used during cement placement in steam injection wells, including conventional and foamed cement, lightweight cement, and flexible cement composites. Laboratory experiments have shown that foam and lightweight cement composites both demonstrate a lower average Young's modulus than conventional cement. However, mechanical stress simulations predict failure of foam and lightweight cement systems in the typical steam injection environment. In these simulations, cement failure occurred under traction and/or compression, with the fracture propagating in the direction of the principle, radial stress, due to expansion or compression of the inner casing and due to Mohr-Colomb forces acting on the cement. Current cement composites that contain extenders that also provide set cement flexibility are not stable at the high temperatures at which steam is used in some heavy oil recovery wells. Although typical flexible cement composites (TFCC) were designed to distribute downhole stresses more evenly than conventional, foamed, or lightweight cements, they cannot withstand temperatures greater than about 550° F. (288° C.), which are typically associated with steam injection. Rapid degradation would occur after exposure to these temperatures. Extenders that can provide flexibility after extended exposure to high-pressure steam would be desirable.